1. Field of Invention
The present invention relates to an improved system for sensing, receiving, and processing reflected energy signals such as laser light pulses. More specifically, the invention concerns a detecting and ranging system for transmitting pulses of energy, detecting energy signals and efficiently identifying a reflected "return" signal within the detected signals with reduced processing time and reduced memory usage.
2. Description of Related Art
Many different systems have been used in the past to intelligently guide projectiles such as missiles. After the laser was developed, the defense industry put laser technology to use in the form of laser detecting and ranging (LADAR) guidance systems.
In LADAR guidance systems, brief laser pulses are generated and transmitted via a scanning mechanism. Some of the transmitted pulses striking a target of interest are reflected back to a receiver associated with the transmitter. Such LADAR systems are commonly installed in projectiles such as missiles to determine the type-and location of a target. The target and surrounding area are scanned to produce an image that comprises multiple pixels. The image can then be analyzed to extract three-dimensional targeting information. The time between the transmission of a laser pulse and the receipt of the reflected laser pulse ("return pulse") is used to calculate each pixel's range.
In known LADAR systems, electronic circuitry begins a ramp function concurrently with the transmission of the outgoing pulse. The ramp function is halted when a return pulse is received. Thus, the height of the resulting ramp is directly proportional to the range to the target. Although the contour and magnitude of the return pulse contain useful information, variations may result in uncertainties as to when the ramp function should be stopped.
Ideally, a return pulse has a finite duration, and an analog ranging system terminates the ramp function mid-way through the pulse. But since the magnitude of a pulse cannot be determined in advance, it may be difficult to distinguish a return pulse from other light. Therefore, some systems set a threshold to differentiate between return pulses and other light. This may result in an inaccurate determination of range, especially where the distance between the target and the receiving optics is great, and the return pulse accordingly has a small magnitude.
Other known systems start a counter when a laser pulse is transmitted and terminate the counter when the return pulse is detected. The value of the counter is thus proportional to the distance to the target. This method suffers from some of the same threshold uncertainties as the ramp methods. In addition, the return pulse may be corrupted by noise. Moreover, the width of the return pulse will be changed as a function of the slope of the target. Thus, there remains a need for a system that reduces the uncertainties in determining a range to a target.
Another need exists in this area of technology because engineers that design missile guidance systems are almost always interested in reducing the weight, size, and expense of the associated electronics. In particular, since random access memory ("RAM") modules are often bulky and expensive, it would be desirable to have a missile guidance system that utilizes RAM more efficiently, and therefore requires less RAM.
In designing missile guidance systems, engineers are also concerned with increasing the resolution afforded by such systems. This may be accomplished by increasing the sampling rate of the system, or, in other words, increasing the frequency of the LADAR pulses emitted by the system. In systems that utilize the time between LADAR pulses to analyze stored return signals, increasing the frequency of the pulses requires that the analysis of the stored pulses must be conducted more quickly. Therefore, it would be advantageous to have a missile guidance system that requires less computation time to analyze its return signals.